Cascade trays for an evaporator and a method of filling such trays



0, 1968 P. w. SCHIPPER 3,397,872

CASCADE TRAYS FOR AN EVAPORATOR AND A METHOD OF FILLING sucn TRAYS FiledOct. 18, 1965 2 Sheets-Sheet 1 l N U E N TO 2 L P/ 57-52 W 56/11/3 45?ATTOR EY 8- 0, 1968 P. w. SCHIPPER 3,397,872

CASCADE TRAYS FOR AN EVAPORATOR AND A METHOD OF FILLING SUCH TRAYS FiledOct. 18, 1965 2 Sheets-Sheet 2 INUE To 2 F5 7752 14 JJdH/PX-E? UnitedStates Patent 3,397,872 CASCADE TRAYS FOR AN EVAPORATOR AND A METHOD OFFILLING SUCH TRAYS Pieter W. Schipper, Elm Grove, Wis., assignor, bymesne assignments, to Milwaukee Chaplet & Mfg. Company, Inc, Milwaukee,Wis., a corporation of Wisconsin Filed Oct. 18, 1965, Ser. No. 496,909 9Claims. (Cl. 261-110) ABSTRACT OF THE DISCLOSURE A humidifier which hasa vertically stacked series of cascade trays. The centers of the trayshave interlocking annular depending skirts which act as overflow weirsto control the flow of water to the trays from a feed hopper mountedabove the uppermost tray. The interlocked skirts also act as traps toprevent backflow of water from a tray through the skirts to the nextlower tray.

This invention relates to cascade trays for an evaporator and a methodfor filling such trays. For convenience, the invention will be describedwith particular reference to a humidifier in which water is the liquidto be evaporated, it being understood that the invention has moregeneral application.

In the evaporating system in which the trays are used, the water to beevaporated is introduced into the uppermost tray. As each successivetray is filled, the water flows to the next lower tray in the cascadeseries until, when the water fills the lowermost tray, it spills into abalanced pan which when filled to a certain level and by means of alever system closes the inlet valve.

Cascade trays present problems. First, there is the problem ofcontrolling the level of the liquid in the respective trays. When agiven tray is full, the slightest disturbance will start the waterflowing over its weir. Once the lip of a weir has been wetted, the flowwill continue for considerable time. In the case of a single tray,little difliculty would be presented. In the case of a number of traysas herein illustrated, this after-drip will continue for perhaps twentyminutes.

Secondly, since replenishment of the water is dependent on the status ofthe water level in the balanced pan, the above described phenomenontends to drain water from the trays into the balanced pan, with theresult that, assuming all of the trays and balanced pan to be of likecapacity and area, the trays will tend to evaporate dry before the waterlevel in the balanced pan drops sufliciently to open the inlet valve. Inan effort to solve this problem, cascade trays heretofore have beenprovided with excess water which has thereupon been permitted to drainaway.

The present invention contemplates supplying only such Water as isneeded, and ensuring that all water is evaporated. T 0 that end eachtray is provided with an air lock which has the function of allowingwater to pass to the trays but stops over-run by preventing discharge ofwater over the weirs except in the course of the desired fillingprocess.

To achieve these objectives, it is preferred to use a stack of identicalmolded trays arranged in cascade relation upon a suitable support, thelowermost tray of the cascade series discharging into a counterbalancedpan which operates the intake valve. Each tray has a generally annularweir with a top margin which is not at uniform level for reasonshereinafter explained. The inner surface of the annular weir tapersoutwardly at a slight conical angle so that water overflowing the weirwill flow down the inner surface of the weir to a point of dischargewhich is outside of the weir of the next lower tray in the stack.

Surrounding each such weir there is a dam having its upper margins andsurface somewhat lower than that of 3,397,872 Patented Aug. 20, 1968 theweir. The water received from the next higher tray fills the annularspace between the weir and the dam. A downward extension of the weir ofthe next higher tray extends into this space.

Surrounding the dam is an annular pocket which receives wateroverflowing the dam. This pocket opens into the storage area of thetray. However, a flange depending from the next higher tray encirclesthe top of the dam, extending to a level slightly lower than the top ofthe dam.

The contours of the respective trays provide air traps and ceilings asshown specifically in the drawings and hereinafter described, the objectbeing to prevent discharge from the trays of water which would otherwiseflow in a direction reverse to that of entry into the storage area.

In the drawings:

FIG. 1 is a general view in perspective of a typical humidifierinstallation selected for the purpose of exemplifying the invention.

FIG. 2 is a view partially in side elevation and partially in sectionshowing a typical cascade tray arrangement.

FIG. 3 is a detail view of the top tray and a special filling hopper intransverse section.

FIG. 4 is a plan view of the filling hopper.

FIG. 5 is an inverted plan view of the hopper.

FIG. 6 is a view on a reduced scale showing one of the trays inperspective.

FIG. 7 is an enlarged plan view of the tray shown in FIG. 6.

FIGS. 8 to 13 are enlarged fragmentary detail views in diametrical crosssection illustrating diflerent conditions in the operation of cascadetrays embodying the invention, each such view showing an upper tray anda lower tray in the series. To illustrate a point, the tray shown inFIG. 8 is slightly diflerent mechanically from the other traysillustrated.

As already stated, the invention has to do with cascade trays in Ianevaporator of any sort. Therefore, in limiting this description to ahumidifier, it will be understood that I am using the humidifier as arepresentative device and any reference to water is intended tocomprehend any other liquid sought to be evaporated.

FIG. 1 shows the evaporator casing 14 applied to the side of a hot airplenum chamber 16 on a hot air furnace 18 which has a cold air return at20. Communication between the hot air plenum 16 and the cold air return20 is provided by a conduit 22 and an opening 24 in the hot air plenum.The casing 14 is connected with the plenum about opening 24.

On the top of the casing 14 is a valve chamber 26 in which a valve body28 is disposed, being supplied with water through the supply line 30.Movable to and from a seat in valve body 28 is a valve 32 having on itsstem 34 a float 36. A lever 38 fulcrumed at 40 is pivotally connectedwith the stem and with the link 42 which also serves as a counterweightfor the balanced pan 44. This pan is fulcrumed at 46 and has a knifeedge pivotal connection at 48 with the counterweight 42.

The arrangement is such that when the pan is full, it tilts downwardlyupon its fulcrum as shown in FIG. 2, thereby lifting the counterweightto move the valve 32 to its seat. Thus when the water evaporates fromthe pan 44, the counterweight oscillates the pan clockwise as in FIG. 2,thereby opening the water valve. The flow of Water from the water valveinto the valve casing 26 raises the level of water in the casing untilthe water overflows the gooseneck 50 and starts siphon action.

The general organization thus far described is not claimed herein,having been described by me in U.S. Patent 3,285,27 6.

The cascade trays 52 may all be identical. They are preferably molded ofsynthetic resin and-designed to stack one upon another. The lowermostcascade tray rests upon bracket seats 54 provided in the casing 14 asshown in FIG. 2. This tray discharges directly into the balanced pan 44which controls the valve. The uppermost of these trays can be filleddirectly from the siphon tube 50 but in order to distribute the incomingwater as desired it is preferred to introduce the water into theuppermost tray through a hopper 56 shown in FIGS. 3, 4 and 5. The bottomof this hopper is made to fit the tray parts in the same manner in whichanother superimposed tray would fit corresponding parts. This willhereinafter be described.

Each of the trays 52 comprises a bottom 58 and a side wall 60 whichcompletely surrounds the bottom and provides an enclosed area to retainthe water to be evaporated. The corners of the side wall 60 are built upas at 62 to provide posts upon which the next successive cascade tray ismounted. The posts provide clearance between trays for the circulationof air traversing the evaporator casing -14 between the plenum 16 andthe pipe 22.

Each of the cascade trays 52 is provided in accordance with the presentinvention with a series of integral weirs, dams, channels andcooperating surfaces for the control of water flow between successiveupper and lower trays. FIGS. 8v through 13 are intended to show how thiscontrol is exercised. They also illustrate mechanical structure of theparts involved. Such parts are also shown in FIGS. 3, 6 and 7.

At some intermediate point on the bottom 58 of each tray there is anintegral well 64. The bottom 66 of this well is externally encircled bya flange 68 which extends a short distance below the under surface 70 ofthe bottom wall 66. The lower surface of the well bottom 66 is sorelated to an underlying pan that it will hereinafter sometimes bereferred to as ceiling.

Rising centrally of the well above the bottom wall 66 is a tube 72provided intermediate its height with a horizontal partition wall 74.The portion 76 of the tube 72 which is above wall 74 is hereinafterreferred to as a darn.

Integral with the partition 74 and rising above it is a conicallytapered tubular strucure 78 wihch is hereinafer referred to as a weir.The interior of the weir 78 progressively decreases in cross section inan upward direction. The taper of its internal surface 80 is continuedbelow the partition wall 74 to the point where it merges with agenerally cylindrical band 82 below which the taper is resumed at 84 inapproaching the lower extremity 86. Extremity 86 is well below the levelof the flange 68 as above described.

FIG. 8 shows a construction in which the top margin 88 of the weir 78 ishorizontal. This is not preferred for reasons hereinafter to beexplained. The preferred arrangement is shown in FIGS. 9 to 13 and inFIGS. 3, 6 and 7 where the upper margin 90 is slightly beveled.Alternatively, it may be notched or shouldered as indicated at 92 inFIG. 14, the object being to break the surface tension which, runlessthe opening through the dam were made abnormally large, might cause thedam to be bridged by the liquid to cause flow centrally through the daminstead of in the desired manner of flow down the interior surface. FIG.8 shows the undesirable type of flow bridging the darn at 94 andtrickling at 96 downwardly through the center of dam 78.

As will be observed in FIGS. 8 through 13, the assembled position of thecascade trays is in a stack such that the lower margin 86 of the tube 78of each upper tray surrounds the margin 88 of the dam of the next lowertray and is interposed between the darn 76 and the weir 78 of the nextlower tray. In each case, the downwardly projecting flange 68 of theupper tray encircles the dam 76 of the next lower tray, the ceiling 70of the upper tray lying closely spaced above the margin of the dam 76.Although the upper trays are supported in each instance from thecorresponding corners of the underlying tray, the spacing between traysin the trap area is important enough so that I may use spacing lugs asshown at 77 (FIGS. 6 and 7). These lugs are not shown in FIGS. 8 to 13because the latter are intended to be diagrammatic and the lugs mightobscure the intended operation. In each case, there is an invertedchannel 98 in the upper tray which is just above the channel 100 of thenext lower tray. The provision on ceiling 70 of an annular rib at 102 isa preferred arrangement.

The hopper 56 which receives water from siphon 50 and delivers it intothe uppermost tray in the stack has a depending annular flange 104extending into the channel 100 of the tray at the top of the stack. Thewater entering the hopper is baflied by a web 106 which has openings at108 and 110 to so regulate the flow that the water enters the uppermosttray of the stack in substantially the same manner that the water enterseach successively lower tray in the stack.

Describing now the operation of the system, reference will be made toFIGS. 8 to 13. Each of these figures illustrates two trays 52 which areidentical with each other. For convenience, the uppermost tray in anygiven pair will be called 52A and the lower tray in any pair will becalled 52B.

As already indicated, the desired control of the liquid to be evaporatedcan best be achieved if the liquid cascades from tray to tray. Since allof the openings of these identical trays are alike, it will be apparentthat if the uppermost opening is bridged at the time the uppermost trayis filled (this being indicated at 94 in FIG. 8) the resulting trickle96 will pass through the whole series of trays to the fulcrum pan 44 andthe objective of distributing the liquid uniformly between the severaltrays will be defeated. This bridging cannot occur if the openingsthrough the several weirs are sufficiently large in diameter. However,this would be an extravagant procedure since the size of the trays wouldthen be excessive. The bridging can easily be avoided in trays ofappropriate size by tilting the margin slightly as shown at or byputting a notch or a step 92 in it (FIG. 14) to break up the continuityof surface tension around the edge.

Since FIG. 8 shows an undesirable contingency, the description ofoperation will commence with FIG. 9. The upper tray 52A has had itsWater storage area filled with water 114 to a level which, by reason ofsurface tension, will be slightly above the lowest point of the uppermargin 90 of the weir 78. In reaching the weir, the water will haveflowed over the darn 76 and filled the intervening channel 100.

When the water wets the margin of the weir 78, it will ultimatelycommence to flow downwardly in a stream 116 which will follow theconical inner surface 80, thus being conveyed into channel between theweir 78 and the darn 76 of the lower tray 52B (FIG. 9).

As illustrated in FIG. 10, the water in channel 100 of the lower tray52B has increased to a point such that the water has begun to overflowthe lower dam 76. In so doing, it contacts the so-called ceiling 70 atthe bottom of upper tray 52A. The dimensions are so chosen withreference to the liquid involved that the liquid will actually contactthe ceiling 70 as shown. Assuming that the liquid wets the ceiling, thisactually aids the flow of liquid outwardly from channel 100 toward thestorage area of the tray. Due to surface tension, water (for example)will stand one-eighth to three-sixteenths inch over the top of such adam before spilling over. Assuming that water is the liquid handled, andassuming that the ceiling is brought down to a level such that it willbe engaged by the water, the water will wet the ceiling and, by surfacetension, will actually pull itself across the dam and start flowing intothe channel 64 outside the dam.

The skirts 86, 68 of the upper tray and the dam 76 of the lower traytogether provide an annular inverted U- tube 75 with a longer inner legbetween the skirt 86 and the darn 76 and a shorter outer leg between thedam 76 and the skirt 68. The inverted channel 98 rises above the innerleg and serves to trap air under the conditions shown inFIGS. and 11.

In FIG. 10, air has been trapped in the inverted channel 98 of the uppertray and air has been trapped at 120 in the top of the shorter outer legof the U-tube 75 between the dam 76 of the lower tray and the dependingflange 68 of the upper tray of the stack. The back pressure produced bythe 'trapped air has caused the water level to rise at 122 to a pointsuch that only surface tension prevents it from rising over the topmargin 90 of the weir 78 of the lower tray 52B. The water is beginningto fill the storage and evaporation space in the lower tray as indicatedat 124.

FIG. 11 shows a situation which arises when the water level 126 in thelower tray is high enough to create a head which forces the water 128 toflow over the edge 90 of the weir 78 of lower tray 528 to flow down at116 along the outwardly tapering side wall 80 thereof and to enter thenext successively lower tray in repetition of the sequence justdescribed. The sequence will be repeated until all of the trays in thestack receive water. When the water begins to spill over the lip 90 ofthe weir of a given tray, practically all water received by that traythereafter is passed on to the tray beneath it, none of it going throughthe U-tube into the tray just filled. This is the situation which existsin FIG. 11.

After the supply of water has been cut off by the closing of the valveat 32, it is desired that all flow downwardly from the respective traysshall be promptly discontinued so that thereafter the water willevaporate from the trays instead of being discharged physicallytherefrom. FIGS. 12 and 13 show how the air locks above describedprevent the water from continuing to flow over the weirs in the mannerwhich has happened in cascade tray structures of the prior art.

The volume of air trapped in the U-tube in relation to the volume of theinner leg of the U-tube and the relative length of the outer and innerskirts 68 and 86 are all important. In the actual tray herein disclosed,which is designed for the vaporation of water, the dam 76 has a heightwhich is one-eighth inch lower than that of the weir lip 90. Constructedas shown, the operation of the U-tube is so effective that if water isintroduced into the tray by external means (instead of arriving throughthe U-tube) it will flow over the side of the tray before spilling overthe weir, despite the fact that the weir is threeeighths inches lowerthan the side. The reasons for this will be shown below in discussingFIG. 13.

The effective pressure on the inner leg of the annular U-tube 75 exceedsatmospheric pressure by the dimension shown at h in FIG. 12. Thepressure to which the outer leg of the annular U-tube 75 is subject isin excess of atmospheric by the dimension indicated at k in FIG. 12.Surface tension is ignored in both instances. Equilibrium is reachedwhen h and k are equal. As clearly appears in FIG. 12, this will occurwhen the liquid 126 in the tray outside of the tube is considerablyabove the level 129 that equals the level of the lip 90 of the weir 78.Thus the U-tube holds the water level in the tray outside of the trapdespite the fact that the wetted surface 90 at the edge of the weirdrains off such water as has accumulated at the top of the weir insidethe skirt 86.

As shown in FIG. 13, the parts are so dimensioned that the outer leg ofthe annular U-tube 75 will be substantially completely purged of airbefore the water within the tray 52B reaches the top of the dam 76. 12represents the distance that the level 130 is above the level of dam 76.k represents the distance that the lip 90 of the weir 78 is above thelevel of the lower margin of the skirt 86. Water level 130 cannot reacha level such that head in is greater than head h Thus reverse flow isimpossible. In practice, h is three-eighths of an inch and since the damis oneeighth of an inch below the lip 90, it never happens that thewater can flow inwardly from the tray 52B over the weir lip of the nextlower tray. (As in the previous examples, surface tension is beingignored.)

Due to surface tension, the liquid would actually have to be raisedoutside of the trap considerably higher than illustrated before flowcould occur in an inward direction. Also liquid clinging to the ceiling70 acts to resist flow. Tests show that water will actually run over thesides of the tray before spilling over the weir of the next lower tray.

The sharp ridge 102 depending from the ceiling 70 prevents the waterfrom clinging to the ceiling when its movement is outward. If the liquidwere other than water, or perhaps consisted in water having a wetttingagent therein, or a material tending to adhere to a plastic tray, airmight be driven from the air lock in the absence of a ridge such as thatshown at 102.

In actual practice, trays which have skirts and flanges interacting toestablish the U-tube and air locks functioning as above described areeffective to permit the trays to fill readily when supplied with Waterabout the central weir, as above described, but resist loss of waterover the weir after that portion of the water which wets the sur face ofthe weir has been delivered downwardly. As a result of the arrangementdescribed, it is possible to fill successive trays in the cascade seriesand yet to ensure that when the valve is closed no further water willescape from any of the trays except by evaporation. Thus the overflowingof the balanced control pan at the bottom of the series is prevented andthe operation of the valve is positive and accurate without anynecessity of supplying excess water which is wasted.

I claim:

1. A plurality of superimposed evaporator trays wherein an upper trayhas inner and outer depending skirts, the inner skirt having its lowerend at a lower level than the outer skirt, the next lower tray having aninner weir within the inner skirt of the upper tray and *an outer darnintervening between the inner skirt and the outer skirt of the uppertray and in outwardly spaced relation to the Weir, the height of theweir exceeding the height of the dam.

2. A plurality of trays in a stack according to claim 1 in which theweir has an inner surface which progressively expands downwardly.

3. A plurality of trays superimposed in a stack, the trays havingsubstantially identical central trap portions which are interrelated inthe stack, the trap portion of each ray including a central well, agenerally annular darn extending upwardly from the center of the well, apartition intermediate the height of the dam, a weir carried by thepartition and surrounded by the dam and projecting to a substantiallyhigher level than the dam, said weir being continued below the dam as adepending skirt and having an inner surface which expands downwardlytoward the bottom of the skirt, the skirt of an upper tray in said stackbeing interposed between the weir and the dam of the next lower tray inthe stack, each tray further having below its said well a ceilingsurface spaced above the dam of the next lower tray in the stack, and asecond skirt depending to a level lower than the top of the dam of saidnext lower tray.

4. An evaporator comprising a stack of trays in superimposedrelationship, and means for introducing into the uppermost tray a liquidto be evaporated, and for filling the trays with such 'liquidsuccessively from the uppermost tray downwardly, means for shutting offthe introduction of liquid when the lowermost tray in the stack hasreceived a charge of liquid, and trap means with which each such tray isprovided for opposing the discharge reversely through the trap of eachtray of liquid introduced therein through the trap means for evaporationfrom the tray.

5. An evaporator according to claim 4 in which the trap means comprisesa darn flange upstanding in the lowor tray, a relatively long innerflange and a relatively short outer flange depending from a superimposedtray and disposed at opposite sides of said dam flange, the superimposedtray being closed between the said depending flanges and having, withsaid depending and dam flanges the form of an inverted U-tube having arelatively longer inner leg and a relatively shorter outer leg, andmeans for guiding into the lower end of the relatively longer inner legthe liquid to be introduced into the respective tray, both legs havingterminal portions immersed in the liquid so introduced.

6. An evaporator according to claim in which the several flanges areannular, the lower tray having a centralannular weir constituting a partof the means for guiding liquid into the longer leg of the U-tube foradmission to the tray, said weir having a top margin at a level higherthan the top of the dam flange and having an inner surface which flaresconically in a downward direction, the top of the weir of one tray lyinginside of the bottom of the weir ot the next higher tray in the stack.

7. An evaporator according to claim 6 in which the top margin of theweir is non-uniform in height and the conical angle of its inner surfaceis sufliciently small so that liquid overflowing the weir will followalong such surface for delivery outside of the weir of the next lowertray.

8. An evaporator tray comprising unitarily a bottom having a centralwell and side walls for holding liquid to be evaporated and providedwith inner and outer depending skirts of which the inner skirtterminates at a lower level than the outer skirt, and further beingprovided with an annular dam having a top margin above the level of thetray bottom, and an annular weir spaced inwardly from and surrounded bythe dam and having a top margin at an elevation higher than the level ofthe top of the dam, said tray being adapted to be stacked with similartrays with the inner skirt of a superimposed tray depending between theweir and the dam of the next lower tray, the dam of the lower trayintervening between the outer skirt of the upper tray and the weir ofthe lower tray, said skirts and weir and dam having the cross-sectionalform of an inverted U -tube when so stacked.

9. A method of tray evaporation of liquid, said method comprising thecascade filling of a plurality of trays in succession, includingself-initiating the fiow of liquid from below the top margin of eachtray into a successively lower tray by conducting the liquid downwardlythrough the centers of the trays and through a series of concentricweirs of concentric weirs depending from the trays, and trapping betweenthe depending weirs in eac tray the liquid filled into such trays,whereby to preclude reverse flow of such liquid from the tray and torequire that such liquid be evaporated as its only means of egress.

' References'Cited UNITED STATES PATENTS lHARRY B. THORNTON, PrimaryExaminer.

E. H. RENNER, Assistant Examiner.

